7.5 open to posi.

I'm buying a new v8 from blueprint to replace my current worn out v8 (no I'm not going to build the current engine because it's much simpler and less confusing than building an engine with unknown specs) 84 ranger and it makes about 390hp. I plan on pairing it up to my current c4 auto and...

I have a 1997 ranger XLT 2.3 2wd. It has the 7.5 OPEN rear end, and i was wondering how hard/what would i need, To put a posi in it. Do i need to replace the whole unit? or can i just swap gears from an explorer? Thanks guys!